1. Home
  2. Embedded Programming
  3. Migrating from MMC to SD card

Migrating from MMC to SD card

Hi all,

We currently have a (client's) product that uses an MMC (SPI mode) for datastorage, the client would like to change this to SD card.

After searching the web, I did find the SD card simplified physical layer spec, but not much else. The

formatting link
site keeps giving me timeouts. I also get the impression that I will need to become a member before I can view any usefull stuff on that site.

From what I understand, it is possible to access an SD card as if it where an MMC (both in SPI mode), with only a minor difference in initialization. Is this true?

The client would also like the possiblity to change to 4-bit mode later on. All signals will be routed through programmable logic. We will not be using any of the security features.

Has anyone found more usefull information on the web? Any tips?

--
Stef    (remove caps, dashes and .invalid from e-mail address to reply by mail)

Everyone is more or less mad on one point.
		-- Rudyard Kipling
Reply to
Stef
Loading thread data ...

You should only have to be an SD member to implement the 'secure' stuff (which, to me, suggests that some "security by obscurity" may be involved --- bad idea!). I don't quite see what your client is trying to gain by this move, though.

--
Hans-Bernhard Broeker (broeker@physik.rwth-aachen.de)
Even if all the snow were burnt, ashes would remain.
Reply to
Hans-Bernhard Broeker

We don't need the secure stuff, so that should not be a problem. But where would I find the complete SD spec minus secure stuff?

Mainly for capacity reasons. They've heard SD's with 4GB are already announced. There is also a concern for he future of MMC, which seems to be loosing terrain.

And because SD and MMC ar physically compatible, they can keep using the MCC and be ready for SD.

--
Stef    (remove caps, dashes and .invalid from e-mail address to reply by mail)

After all my erstwhile dear,
My no longer cherished,
Need we say it was not love,
Just because it perished?
		-- Edna St. Vincent Millay
Reply to
Stef

SanDisk has some publicly available documents. I'm not sure where to find them on their site, but I know I have them archived somewhere... if only I could find them :)

Reply to
Lewin A.R.W. Edwards

If your code implements the MMC spec as documented by Sandisk, it should work with an SD card. You don't have to do any special initialization. When I tested my MMC code with an SD card, the only real "difference" I found was that SD cards tended to be slower in responding to commands; the MMCs I was using always responded in the 8 clock cycles following the command while the SD cards had a longer Ncr: 16 or more clock cycles. But the MMC spec allows Ncr to be 64 clock cycles, so this is still within spec.

--
John W. Temples, III
Reply to
John Temples

If you mean these, I found them. ;-)

formatting link 

--
Stef    (remove caps, dashes and .invalid from e-mail address to reply by mail)

I just remembered something about a TOAD!
Reply to
Stef

It's not my code, so we will have to see but this sounds very promising.

--
Stef    (remove caps, dashes and .invalid from e-mail address to reply by mail)

There's a fine line between courage and foolishness.  Too bad it's not a fence.
Reply to
Stef

document

Reply to
Josep Durán

You can send some more instructions to the SD card once it is initialised, and the SPI will speed up to 25MHz. The slower data rates are so the SD card is compatible with the MMC card. The SD card socket is thinner I think, so that MMC cards can't be used with it, but SD cards can be used with the MMC socket.

Contact your local Sandisk distributor, and ask for the following document:

Sandisk Secure Digital Card Product Manual Version 1.9 (there may be a later version than this) Document Number 80-13-00169 December 2003

You will have to sign an NDA though to get it. Make sure that you check the operation of cards from different manufacturers as well because they may not have exactly the same implementation as Sandisk.

Regards David Milne

Reply to
dmm

No, this document is called something like SD_Architecture_1.0.pdf. Didn't see it on that page you pointed to.

Reply to
Lewin A.R.W. Edwards

No, it's the other way around.

--
John W. Temples, III
Reply to
John Temples

I did also find ProdManualSDCardv1.9.pdf somewhere on the sandisk site. This is a 113 page document that also has things like the register definition.

This document is is also not on the above link, think I found with the search tool.

--
Stef    (remove caps, dashes and .invalid from e-mail address to reply by mail)

There is more simplicity in the man who eats caviar on impulse than in the
man who eats Grape-Nuts on principle.
		-- G.K. Chesterton
Reply to
Stef

For anyone who's interested, the link is

formatting link

MiniSD card

formatting link

Older SD card specs

formatting link

These files are hidden on the SanDisk pages.

Reply to
dmm

ElectronDepot website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.